1. Field of the Invention
The present invention pertains to a method of disposing of oily liquid wastes, in particular, by injecting the waste materials into a fractured subterranean earth formation in an amount which does not exceed the irreducible liquid saturation level of the formation with respect to said oily liquid wastes.
2. Background
Satisfactory disposal of liquid and slurried solids waste materials into subterranean earth formations requires adherence to certain conditions which control the residency of the waste materials in a predetermined zone where the materials are injected. Waste materials may be disposed of in subterranean earth formations by injecting the material in the form of a liquid or a slurry of fine solids particles through an injection well into a predetermined disposal zone by hydraulically fracturing the earth in the disposal zone to accommodate a suitable volume of waste material. In certain areas where contamination by the waste material is not of any concern, that is, for example, the disposal zone is not near a source of usable water, the waste material is merely injected through a hydraulic fracture or, if the earth formation is of a highly permeable, unconsolidated character, the material simply diffuses and disperses into the formation.
However, in areas where it is possible that the waste material may migrate to a source of usable water or usable minerals which would eventually result in the waste material being brought back to the surface as a contaminant in the recovered water or mineral, the designated formation disposal zone must adhere to certain criteria. A U.S. patent application entitled "Waste Disposal in Hydraulically Fractured Earth Formations", Ser. No. 07/910,381, filed Jul. 8, 1992 in the name of Thomas K. Perkins and assigned to the assignee of the present invention discusses certain desirable characteristics of earth formations which can be hydraulically fractured to dispose of solids particulate wastes, in particular, which are slurried and injected in the form of a viscous fluid into the formation. This application discusses the need to define a zone of interest for disposal which is bounded by earth formation zones which have higher in situ compressive stresses so that the hydraulic fracture will be confined to the designated formation zone of interest. Another desirable feature according to the Perkins patent application is the requirement of layers of permeable and relatively impermeable material in the zone of interest which is fractured so that relatively unrestricted flow channels are formed in the fracture to permit disposal of substantial volumes of waste material.
Unfortunately, earth formations having all of the features described in the Perkins patent application are not always available for disposal of wastes through injection wells. However, certain wastes such as oily liquid wastes and similar wastes having water and oil content, or primarily water-like liquid content, may be disposed of in earth formation zones which have other characteristics which will prevent the waste materials from leaving the predetermined formation zone of interest. In accordance with the present invention, a unique disposal method has been discovered which, although may benefit from the characteristics of the Perkins invention, also benefits from another unique formation property with respect to the characteristics of the waste material. The number and volume space of suitable sites available for disposal of the projected and ever-growing volume of liquid waste materials is substantially enhanced by the disposal method of the present invention.